Method and machine for cleaning objects in plate form

ABSTRACT

The invention concerns a method and a machine for cleaning objects in plate form such as screen printing stencils. The method consists in: immersing an object ( 2 ) to be cleaned in a cleansing composition bath consisting of an azeotropic liquid solution having a density not less than the density of residues of average density likely to soil the object ( 2 ), and adapted to loosen the residues from the object ( 2 ) without solubilising them. The object ( 2 ) is placed in a vessel with vertical walls at a distance less than 10 cm from the vertical faces of the object ( 2 ). The treating vessel ( 1 ) spills over into an overflow vessel ( 8 ). The cleansing composition is continuously removed from both vessels ( 1, 8 ), filtered and re-introduced in the treating vessel ( 1 ) top part.

The invention relates to a method and a machine for cleaning objectshaving the general form of plates, such as screens or stencils forscreen printing, notably screen printing stencils used in the productionof electronic circuits for depositing adhesives or solder pastes, andmore particularly stencils for frames, so-called self-tensioning frames,which are simple flexible fragile thin metal foils.

So far, cleaning of such pieces is often realized in practice manuallywith the help of solvents on a duster for the glue, or with the help ofmachines (DE-A-4,010,679) spraying under pressure on the pieces eitheraqueous solutions with saponification agents or solvents (with all thetechnical strains imposed by the use of chemicals with an ignitionpoint). Such devices are cumbersome, represent important investments,and do not allow to clean and separate in one step residues of variouschemical compositions. However, modern regulations on environment imposeto be able to separate residues to allow their recycling, theirinerting, or their later destruction according to their chemicalcomposition.

So, with these devices, it is necessary to provide a rinsing step and aresidue sorting/separating step. Moreover, the cleansing solutions loadwith residues and must be regularly renewed, which is expensive andharmful to environment.

Further, these devices do not allow to clean the stencils forself-tensioning frames, which are too fragile for a manual rub cleaningor a pressure spray cleaning.

So, effective technical cleansing compositions are known such as VIGON®SC 200 marketed by the company Dr. O.K. WACK for spray cleaning ofscreen printing stencils, which has the advantage of eliminating at roomtemperature adhesives used for surface mounting of components (CMS) andsolder pastes, and which is not inflammable. This composition based onwater-dissolved alcoxypropanols forms a microphase at a temperaturebetween 20 and 30° C. It is recommended by the manufacturer, afterapplying the fluid by spraying on objects to be cleaned, to rinse withwater. With these compositions, it is noted that the spray-treatmenttime for each piece is in general more than 1 hour, drying included.

Document PATENT ABSTRACTS OF JAPAN, vol. 95, no. 8, Sep. 29^(th) 1995 &JP 07116617 describes a cleaning method and a cleaning machine in whichan object is immersed in a cleansing liquid which flows from the bottomup in the treating vessel, spills over into a peripheral overflowvessel, carrying along residues in suspense, and is recycled, afterfiltering, in the treating vessel bottom part. Precipitated residues ofhigh granularity are extracted because of a high flow rate from thebottom part of the treatment vessel, and then filtered and recycled.This device does not allow in practice to clean pieces and to separateresidues of low density, of residues of average density and of residuesof high density with an efficiency and a time compatible with industrialoperating stresses. Particularly, this device does not allow to separateresidues from successive or alternative treatments of pieces soiled withsolder pastes (light and heavy residues), and then of pieces soiled withadhesive (residue of average density). Particularly, it is to be notedthat the device according to this document does not particularly allowto separate residues of low density from other residues, notably fromresidues of average density in suspense. This separation is indeed themost difficult one to realize, but it is important, notably insomuch asresidues of low density such as fluxes or fats have a chemicalcomposition very different from that of residues of average density suchas epoxy glue, and thus need later different treatments. Further, thisdevice which does not comprise any heating means does not allow to use aliquid susceptible of forming a microphase. It works thus either as asolvent, or as a surfactant. Consequently, in such a device, thecleansing liquid dissolves residues, and must thus be regularly renewed,which is expensive and harmful to environment.

The invention aims thus to solve these drawbacks by providing a methodand a machine for cleaning objects having the general form of plates,such as screen printing stencils, which can be soiled with residues ofaverage density, notably of density of the order of 1, and/or with solidresidues of high density, notably of density not less than 1, and/orwith residues of low density, notably of density less than 1, and thisunder economical conditions compatible with an industrial use, andallowing to separate at least residues of low density.

More particularly, the invention aims to allow to automatically separateresidues according to their density, after indifferently successive oralternative treatments of a number of different pieces soiled withresidues of any density. Particularly, the invention aims to allow toalternatively treat pieces soiled with residues of low density and withresidues of high density, such as screen printing stencils soiled withsolder pastes (including fluxes of low density and metal alloy particlesof high density), and pieces soiled with residues of average densitysuch as screen printing stencils soiled with glue (residue of averagedensity), and to separate these different residues according to theirdensity at the time of each treatment, without maintenance between twotreatments of distinct pieces.

The invention aims thus to allow to treat successively or alternativelypieces soiled with various residues (indifferently of low, high oraverage density), without any waiting time between pieces.

Particularly, the invention aims to allow to avoid to realize thedistinct subsequent steps consisting in rinsing and separating residues,and permanently renewing the used cleansing composition.

The invention aims also to provide a method and a machine which has alow cost-investment, is simple and economical to use and provides a highcleansing efficiency. Particularly, the invention aims to enable acomplete treatment (cleansing and drying) with a treatment time lessthan 1 hour, notably of the order of 0.5 hour, per object.

The invention aims to enable to clean any kind of objects, includedfragile objects, such as stencils for self-tensioning frames, soiledwith various very resistant residues adhering to the object such asmetal particles (solder alloys), solder fluxes, fats, adhesives (epoxyglues, adhesives for CMS, . . . ).

For so doing, the invention relates to a method for cleaning objectshaving the general form of plates, such as screen printing stencilssusceptible of being soiled with residues of average density such asadhesive particles, and/or with solid residues of high density such asmetal particles, and/or with residues of low density such as solderfluxes or fats, in which at least one object to be cleaned is immersedin a vessel, so-called treating vessel, filled with a liquid cleansingcomposition, at least one of vertical walls of the treating vessel,so-called overflow wall, being adapted to form an overflow containerinto a second adjacent vessel, so-called overflow vessel, the overflowwall being common to the treating vessel and the overflow vessel, atleast one flow Q1 of cleansing composition is continuously extractedfrom the treating vessel and reintroduced into the treating vessel aftera passage through filtering means for filtering residues, and a flow Q2of cleansing composition is continuously extracted from the overflowvessel and reintroduced into the treating vessel after a passage throughfiltering means for filtering residues, characterized in that:

it is used a cleansing composition formed of a liquid azeotropicsolution of a density at least substantially equal to the density ofresidues of average density, adapted to loose residues from the objectwithout solubilizing them,

at least one object is placed vertically into a treating vessel adaptedto have at least substantially vertical walls, so-called verticallongitudinal walls, spaced by a distance less than 10cm, from the mainfaces, disposed at least substantially vertically, so-called verticalfaces, of an object to be cleaned.

the cleansing composition is continuously extracted from the bottom partof the treating vessel and is continuously extracted from the overflowvessel, and the whole cleansing composition extracted from both vesselsis continuously reintroduced in the top part of the treating vessel,after a passage through said filtering means, the object being immersedinto the cleansing composition which continuously flows in the treatingvessel along the object downwards with a flow Q1 adapted to:

allow the cleansing composition to produce its effects on residues byloosing them from the object,

allow the cleansing composition to carry along residues of averagedensity and residues of high density,

allow flotation of residues of low density and their overflow separationinto the overflow vessel, so that in one continuous step residues areloosed from the object, at least residues of low density are separated,and residues of the cleansing composition which does not load withresidues are extracted.

It is to be noted that a method according to the invention isadvantageously applicable to objects having at least as a whole the formof plane plates, the treating vessel having the form of aparallelepiped. Nevertheless, the invention is also applicable toobjects which have not strictly the form of plane plates (wavy,cylindrical or hemi-cylindrical plates . . . ). The form of the walls ofthe treating vessel is adapted to that of objects to be cleaned, so asto have vertical longitudinal walls with forms substantiallycorresponding to those of main vertical faces of the objects.Advantageously, the objects have main faces in the form of ruled surface(plane, cylinder or portion of cylinder with a circular base or with abase of any form), and the vertical walls of the treating vessel have asimilar form.

As the cleansing composition is azeotropic, it is eliminated from theobject by simple evaporation (by natural convection or by hot-airdrying) without trace. As its density corresponds to that of residues ofaverage density, it carries along these residues in its movement.Residues of high density flow to the bottom of the treating vessel andare carried along with the cleansing composition extracted from thebottom part of the treating vessel.

The cleansing composition is adapted not to solubilize residues, andthus does not load with residues. Advantageously and according to theinvention, it is used a cleansing composition formed of an aqueoussolution having the effect of loosing residues from the object withoutsolubilizing them.

Advantageously and according to the invention, the cleansing compositionis an uninflammable solution.

In the case of screen printing stencils, residues of average density areglues of density close to 1, residues of low density are fluxes ofsolder pastes or fats, residues of high density are particles of metalweld or solder alloys or those of conductive glues. Advantageously andaccording to the invention, it is used a cleansing composition thedensity of which is of the order of 1.

Advantageously and according to the invention, it is used a cleansingcomposition formed of an aqueous solution of at least one constituentforming a microphase, notably at least an alcoxyalcohol, at atemperature less than 50° C., and the cleansing composition ismaintained at a treatment temperature adapted to enable the microphaseformation, notably less than 50° C. It is known indeed that in such anaqueous solution in the microphase state, microbubbles ofalcoxyalcohol(s) are formed in water, and have an importantdecomposition power with regard to residues by suppressing theiradherence on the support, without nevertheless solubilizing them as asurfactant. For example, it can be used a composition formed ofapproximately 90% (in weight) and 10% (in weight) of at least oneconstituent among a propylen glycol ether, such as propylen glycolmethyl ether and/or a dipropylen glycol monoether; a polypropylen glycolether, an alcoxypropanol, such as ethoxypropoxypropanol and/orn-butoxypropanol. Particularly, advantageously and according to theinvention, it is used an aqueous solution saturated with at least acleaning agent as described in U.S. Pat. No. 5,486,314.

As the cleansing composition can be used at low temperature (less than50° C., notably between 20° C. and 30° C.), any polymerization,reticulation or hardening process, started by residues heating, isavoided, which helps the cleaning.

Advantageously and according to the invention, VIGON®SC200 marketed bythe firm Dr O.K. Wack Chemie GmbH (Ingolstadt, Germany) is used as acleansing composition, the exact chemical composition of which is notknown. The density of this cleansing composition is equal to 1.Nevertheless, it is to be noted that, contrary to manufacturer'srecommendations, the inventor has surprisingly noted that thiscomposition is highly efficient when used in bath form, i.e. even in theabsence of spray supply of mechanical power. It forms a microphasebetween 20° C. and 30° C.

In other respects, advantageously and according to the invention, thecleansing composition is supplied again by spraying on the free surfaceof the cleansing composition contained in the treating vessel, from atleast one spraying ramp, disposed at a height superior to that of theoverflow wall. Advantageously and according to the invention, thecleansing composition is diffused across said free surface.Advantageously and according to the invention, it is used two sprayingramps parallel one to another, jets formed by one ramp intersectingthose formed by the other ramp immediately over or at the level of saidfree surface so as to form a cleansing composition screen having theeffect of rinsing an object being extracted from the treating vessel.

Advantageously and according to the invention, the flow Q1 of cleansingcomposition extracted from the treating vessel is adapted so that theretention time in the treating vessel is comprised between 30 secondsand 5 minutes, notably of the order of 2 to 4 minutes. This flow Q1 isadapted to allow the cleansing composition to carrying along residues ofaverage and/or high density, but also to enable the counter-flowflotation of residues of low density and their filter separation throughspecific filtering means, and for the cleansing composition to be ableto produce its effects on the residues. The value of this flow Q1 can beempirically adjusted by means of tests according to the residue nature,the form of the object and of the treating vessel.

Advantageously and according to the invention, it is used a treatingvessel adapted to have vertical longitudinal walls spaced from thevertical main faces of the object by a distance comprised between 1 and5 cm, notably of the order of 2 to 3 cm. The distance separating thevertical walls of the treating vessel from the faces of the object is asreduced as possible, so as to realize as far as possible in the treatingvessel a slow and homogenous flow free of cleansing compositionturbulence, and to minimize the quantity of cleansing composition usedin the machine.

Indeed, contrary to what the state of the art indicates, the use of asmall quantity of cleansing composition has many advantages. As such, itis to be noted that the time necessary for the cleansing composition tobe completely filtered and free of all its residues after a treatmentoperation of a piece is very short (of the order of one minute). Everynew piece to be treated is thus immersed into a cleansing compositionfree of any contamination. Pieces soiled with residues varying from onepiece to another can thus successively or alternately be treated withouttaking risk in contaminating one piece with the residues of anotherpiece that has already been treated, or of interaction of residues ofone piece with those of another piece that has already been treated.

Further, advantageously and according to the invention, ultrasonic wavesare emitted in the treating vessel in one direction at leastsubstantially perpendicular to the main plane of an object placed in thetreating vessel.

Particularly, these ultrasonic waves facilitate the action of thecleansing composition in the interstices or the microperforations in theobject.

The invention also applies to a machine for working a process accordingto the invention.

The invention also relates to a machine for cleaning objects having thegeneral form of plates, such as screen printing stencils, susceptible ofbeing soiled with residues of average density such as glue particles,and/or with solid residues of high density such as metal particles,and/or with residues of low density such as solder fluxes or fats,comprising a vessel, so-called treating vessel, adapted to be able tocontain a liquid cleansing composition, and at least an object to becleaned immersed into this cleansing composition, at least one of thevertical walls of the treating vessel, so-called overflow wall, beingadapted to form an overflow container into a second adjacent vessel,so-called overflow vessel, the overflow wall being common to thetreating vessel and the overflow vessel, means, so-called firstcirculation means, for continuously extracting at least one flow Q1 ofcleansing composition from the treating vessel and for continuouslyreintroducing it into the treating vessel after a passage throughfiltering means for filtering residues, and means, so-called secondcirculation means, for continuously extracting a flow Q2 of cleansingcomposition from the overflow vessel, and for continuously reintroducingit into the treating vessel after a passage through filtering means forfiltering residues, characterized in that:

the treating vessel is adapted to receive at least one object to becleaned in a vertical position, and to have at least substantiallyvertical walls, so-called vertical longitudinal walls, spaced by adistance less than 10cm from main faces, so-called vertical faces,disposed at least substantially vertically, of an object to be cleaned,

first circulation means are adapted to continuously extract thecleansing composition from the bottom part of the treating vessel and tocontinuously reintroduce it in the top part of the treating vessel,

second circulation means are adapted to reintroduce in the top part ofthe treating vessel the cleansing composition extracted from theoverflow vessel,

first circulation means are adapted to maintain in the treating vesseland along the object, a flow Q1 of cleansing composition flowingdownwards and adapted to:

allow the cleansing composition to produce its effects on the residuesby loosing them from the object,

allow the cleansing composition to carry along residues of averagedensity and residues of high density,

allow flotation of residues of low density and their overflow separationinto the overflow vessel, so that as the cleansing composition is formedof a liquid azeotropic solution of a density at least substantiallyequal to the density of residues of average density, and is adapted toloose the residues from the object without solubilizing them, in onecontinuous step, residues are loosed from the object, at least residuesof low density are separated, and residues of the cleansing compositionwhich does not load with residues is extracted.

Advantageously, the machine according to the invention comprises atleast one spraying ramp for spraying the cleansing composition onto thefree surface of the cleansing composition contained in the treatingvessel, this spraying ramp being disposed at a height superior to thatof the overflow wall. Advantageously and according to the invention, itcomprises two spraying ramps parallel one to another, jets formed by oneramp intersecting those of the other ramp immediately above or at thelevel of said free surface so as to form a cleansing composition screenhaving the effect of rinsing an object being extracted from the treatingvessel. Advantageously and according to the invention, the sprayingramps are disposed at least substantially above and perpendicularly tothe extreme upper edges of two vertical longitudinal walls of thetreating vessel, at least one of which forms the overflow wall.Advantageously and according to the invention, a first spraying rampbelongs to first circulation means and a second spraying ramp belongs tosecond circulation means.

Advantageously and according to the invention, the overflow wall isformed of one of the vertical longitudinal walls of the treating vesselthe extreme upper edge of which is at a height inferior to that of theextreme upper edges of the other vertical walls of the treating vessel.

Advantageously and according to the invention, the treating vessel isadapted to have vertical longitudinal walls spaced from vertical mainfaces by a distance comprised between 1 and 5 cm, notably of the orderof 2 to 4 cm.

Advantageously and according to the invention, the machine comprisesemission means for emitting ultrasonic waves associated to at least oneof the vertical longitudinal walls of the treating vessel so as to emitultrasonic waves in the treating vessel in a direction at leastsubstantially perpendicular to a main plane of an object placed in thetreating vessel.

Advantageously and according to the invention, first and/or secondcirculation means comprise thermoregulated heating means for heating thecleansing composition, disposed below filtering means for filteringresidues, and above reintroduction means for reintroducing the cleansingcomposition in the top part of the treating vessel.

Advantageously and according to the invention, first circulation meanscomprise a filter, so-called first filter, and a pump, so-called firstpump, and second circulation means comprise a filter, so-called secondfilter, and a pump, so-called second pump. The first and second filtersare similar, and the first and second pumps are similar.

It is to be noted that first circulation means can comprise only oneoutflow port for the cleansing composition in the bottom part of thetreating vessel, and only one filter able to filter residues of averagedensity and to retain residues of high density, while separating them,notably by decantation. For example, this filter can be formed of acontainer including a cylindrical filtering cartridge through which aliquid to be filtered radially passes. This variant is applicableadvantageously when pieces, such as stencils soiled with solder pastesand then pieces soiled with glue are equally well successively oralternately treated. Indeed, in this case, the same filter retains inthe container bottom part residues of high density (particles) which itreceives when the piece being treated is soiled with solder paste (theseresidues falling down to the bottom of the container under gravity), andthen retains in its cartridge residues of average density which itreceives when the piece being treated is soiled with glue (residuesbeing in suspense in the liquid). As such, it is to be noted that, asindicated above, the small quantity of cleansing composition allows totreat successively or alternatively pieces soiled with various residues,with a short waiting time between each piece.

In a variant, two separate outflow ports can be provided, one of whichin the bottom part of the treating vessel supplies a filter able tofilter residues of high density, whereas the other, situated at an upperlevel (above the bottom wall of the treating vessel, but nevertheless inthe lower part of the treating vessel), supplies another filter able tofilter residues of average density. In another variant, an outflow portcan be advantageously provided at half height in one of the verticallongitudinal walls of the treating vessel so as to generate a liquidcomposition flow at least substantially perpendicular to the verticalfaces of the object, e.g. in order to facilitate the passage of thecleansing composition through the through ports or perforations in theobject and the carrying-along of residues which are incrusted therein.

In all cases, residues of low density are separated in a distinctspecific filter of second circulation means.

Advantageously and according to the invention, the treating vessel hasthe form of a parallelepiped, the width of which is comprised between 3cm and 10 cm, notably of the order of 5 cm or 6 cm, and has a volumecomprised between 10 l and 100 l, notably of the order of 50 l. Theheight of the treating vessel is at least equal to that of the objectsto be cleaned.

Further, advantageously and according to the invention, the machinecomprises a suspension frame for suspending an object having the form ofa flexible plate in the treating vessel, this suspension frame beingadapted to receive and maintain the peripheral edges of the object.

The invention also relates a method and a machine characterized incombination by all or part of the above-mentioned or below-mentionedfeatures.

Other objects, characteristics and advantages of the invention will beapparent from the following description of one of its embodiments, whichis only illustrative and non limitative of the invention, with referenceto the annexed drawings in which:

FIG. 1 is a schematic representation of the general principle of amethod and a machine according to the invention,

FIGS. 2 and 3 are respectively schematic top and front views of amachine according to the invention the outer casing of which is notrepresented, so as to allow to visualize its main components,

FIG. 4 is a schematic perspective view of a suspension frame of anobject having the form of a flexible plate to be placed in the treatingvessel of a machine according to the invention.

The machine according to the invention comprises a treating vessel 1adapted to be able to contain a liquid cleansing composition and atleast one object 2 to be cleaned having the general form of a plate suchas a screen printing pencil immersed in this cleansing composition. Thistreating vessel 1 is formed of metal walls in stainless steel and has asa whole the form of a parallelepiped. It comprises a verticallongitudinal outer wall 3, a horizontal lower bottom wall 4, a verticallongitudinal wall 5, so-called overflow wall 5, the extreme upper edge 6of which is at a height inferior to that of the extreme upper edge 7 ofthe vertical longitudinal outer wall 3, so that the liquid cleansingcomposition contained in the treating vessel 1 spills over this extremeupper edge 6 to flow into an overflow vessel 8 adjacent to the treatingvessel 1, the overflow wall 5 being a vertical longitudinal wall commonto the treating vessel 1 and to the overflow vessel 8. The overflow wall5 is parallel to and in front of the vertical longitudinal outer wall 3.

In the example represented in FIG. 1, the overflow vessel 8 is less highthan the treating vessel 1. The overflow vessel 8 is defined by avertical longitudinal outer wall 9 which has preferentially an extremeupper edge 10 at a level at least substantially equal to that of theextreme upper edge 7 of the vertical longitudinal outer wall 3 of thetreating vessel 1. Both vessels 1, 8 are laterally closed by lateralvertical walls 11, 12. Both vessels 1, 8 are open upwards. The bottomwall 13 of the overflow vessel 8 is at a height superior to the bottomwall 4 of the treating vessel 1. The vertical longitudinal outer wall 9of the overflow vessel 8 is provided with a level sensor 14 which allowsto stop the machine operation if the liquid composition level in theoverflow vessel 8 becomes lower than the value predetermined by thissensor 14.

The vertical longitudinal outer wall 3 of the treating vessel 1 isprovided with transducers 15, ultrasonic emitters, regularly distributedon the surface of this wall 3. The ultrasonic emitters 15 are suppliedby a generator 16 controlled by an electronic control device 17 forcontrolling the operation of the machine according to the invention.Particularly, this electronic control device 17 incorporates a timer forthe operation of the transducers 15, emitting ultrasonic waves.

As seen in FIG. 1, the object 2 to be cleaned is positioned in an atleast substantially medial part of the treating vessel 1, at halfdistance from the vertical longitudinal outer wall 3 and from theoverflow wall 5, so that a cleansing composition flow flows verticallydownwards along each of the vertical faces 18, 19 of the object 2. Theobject 2 is placed in the treating vessel 1 so as not to come in contactwith the bottom wall 4. For so doing, it is suspended in the treatingvessel 1 by any appropriate suspension device, e.g. one or moresuspension hooks cooperative with the extreme upper edges 6, 7 of thevertical longitudinal walls 3, 5 and/or the vertical lateral walls 11,12.

The extreme upper edges 20, 21 of the vertical lateral walls 11, 12 arepreferentially at the same level than the extreme upper edges 7, 10 ofthe vertical longitudinal outer walls 3, 9 of the vessels 1, 8.

The treating vessel 1 can be provided with cross-members connecting theextreme upper edges 6, 7 of its vertical longitudinal walls 3, 5 tofacilitate the suspension of objects 2 to be cleaned.

FIG. 4 represents an accessory element allowing to suspend in thetreating vessel 1 an object having the form of a thin flexible metalplate, such as a screen printing stencil for a self-tensioning frame.This accessory element is formed of a frame 22 comprising two verticalslide-like posts 23 adapted to receive the vertical peripheral edges 24of the object 2. Both posts 23 are connected together in the upper partby an upper cross-member 25 welded to these posts 23, and the ends ofwhich project laterally from the post 23 to form suspension tabs 26 ableto rest on the cross-members of the treating vessel 1 or on the extremeupper edges 20, 21 of its vertical lateral walls 1, 12. Two parallelcross-members 25, one on each side, can be provided in a non-representedvariant.

In the lower part, a cross-member 27 connects also the lower ends of theposts 23. The lower ends of these posts can be closed and welded so asto prevent the sliding of the object 2 beyond these ends. Twocross-members 27 can be provided, in a non-represented variant, one oneach side. It is also possible to weld the ends of the cross-element 27inside the lower end of each slide-like post 23 to close the lower endthereof.

The cleansing composition is extracted from the lower part of thetreating vessel 1 and of the overflow vessel 8, filtered, andreintroduced in the top part of the treating vessel 1.

Thus, the treating vessel 1 comprises an outflow port 28 for thecleansing composition provided near the bottom wall 4 of the treatingvessel 1, or even in this bottom wall 4, and through which the cleansingcomposition is extracted. This port 28 is connected via a valve 29 to aline in which are interposed a filter 31, and then a pump 32 whichsupplies the cleansing composition to a heater 33. At the output of theheater 33, the line 30 supplies a spraying ramp 34 disposed above theextreme upper edge 7 of the vertical longitudinal outer wall 3 of thetreating vessel 1.

The filter 31 is adapted to retain residues of average density as wellas residues of high density, extracted from the bottom of the treatingvessel 1 with the cleansing composition. This filter 31 is for exampleformed of a cylindrical decanting container containing a cylindricalhollow filtering cartridge through which the composition to be filteredradially passes in a known per se manner.

The pump 32 is an electric pump which is chosen to provide a nominalflow such that the flow Q1 of the cleansing composition extracted fromthe treating vessel 1 corresponds to a retention time in the treatingvessel 1 comprised between 30 seconds and 5 minutes, notably of theorder of 2 to 4 minutes, and this in view of the head loss in thecircuit. For example, for a treating vessel 1 of the order of 40 l, apump 32 with a nominal flow of the order of 20 l/minute allows aretention time of 2 to 4 minutes for the cleansing composition in thetreating vessel 1.

The heater 33 can be formed of an hollow cylinder partitioned so as toform baffles and can be surrounded by a resistor, all of this beingquilted. The electronic control device 17 is adapted to control theoperation of the electric pump 32 and of the heater 33.

Thus, first circulation means 28, 29, 30, 31, 32, 33, 34 for circulatingthe cleansing composition in the treatment vessel 1 are realized.

Similarly, an outflow port 35 is provided at the bottom of the overflowvessel 8. This outflow port 35 is connected to a line 36 via a valve 37.In this line 36 are also interposed a filter 38, and an electric pump 39which supplies the cleansing composition to the heater 33, and then to asecond spraying ramp 40 disposed above the extreme vertical edge 6 ofthe overflow wall 5. The assembly 35, 36, 37, 38, 39, 33, 40 formssecond circulation means for circulating the cleansing compositionallowing to extract continuously a cleansing composition flow Q2 fromthe overflow vessel 8 and to continuously reintroduce it into thetreating vessel 1 after a passage through a filter 38, which is adaptedto retain residues of low density.

Both spraying ramps 34, 40 are parallel one to another and are providedwith nozzles (FIG. 2) regularly distributed on their entire length andoriented downwards and inclined approximately 45° from the horizontal(FIG. 1) inwardly in the treating vessel 1. Each nozzle of a ramp 34, 40preferentially forms a divergent flaring jet extending at leastsubstantially in a plane inclined downwards for example by approximately45°, inwardly in the treating vessel 1, and to the jets exiting thenozzles of the other ramp 40, 34. In that way, various jets exitingvarious nozzles of a common ramp 34 or 40 intersect before contactingthe free upper surface 41 of the cleansing composition bath contained inthe treating vessel 1. Also, the jets exiting both ramps 34, 40intersect at a level situated above the free upper surface 41. Theresult is that the cleansing composition is homogeneously diffusedacross free upper surface 41 of the cleansing composition bath. Further,when the object 2 is extracted vertically upwards from the treatingvessel 1 after its cleaning, the cleansing composition jets exiting bothramps 34, 40 form a screen through which the object 2 passes, which isthus automatically rinsed on its both faces during its extraction fromthe treating vessel 1. The spraying ramps 34, 40 do not spray directlythe object 2 to be cleaned, but only the free surface 41 of thecleansing composition bath in which the object 2 is immersed.

Advantageously, both pumps 32, 39 are similar, so that the flow Q1extracted from the treating vessel and the flow Q2 extracted from theoverflow vessel 8 are similar.

When the machine according to the invention is started, the treatingvessel 1 is filled with the cleansing composition until it spills overthe overflow wall 5 into the overflow vessel 8 into which a sufficientquantity of cleansing composition is also introduced so that thecleansing composition level in this overflow vessel 8 is above thesensor 14 and the valves 29, 37 are opened. The machine is then startedby energizing the electronic control device 17 by means of anappropriate outer control button. The electronic control device 17controls the operation of the heater 33, of the ultrasonic generator 16,and the pumps 32, 39.

In a non-represented variant, it can also be provided at least a thirdcirculation circuit removing the cleansing composition either at halfheight, or slightly above the bottom wall 4 of the treating vessel 1,but at a level corresponding at least substantially to the lower part ofthe object 2 placed in the treating vessel 1. In that way, residues ofaverage density can be extracted, separated and filtered separately. Itis then provided a specific filter which can be supplied by means of thesame electric pump 32, or a third pump leading to the heater 33 and tothe ramp 34.

As seen in FIGS. 2 and 3, the machine according to the invention can berealized in a particularly compact and cheap form.

Further, it is possible to place side by side several objects 2 to becleaned in the same treating vessel 1, the width of which will be thenadapted to this purpose. Several objects can thus be cleanedsimultaneously in the same machine. Several ramps or pairs of ramps 34,40 can be then provided.

Moreover, the machine can be provided with a receptacle for the cleanedobjects 2 in view of drying them. This receptacle can be supplied withair by means of an appropriate fan. It is to be noted that the cleansingcomposition remaining on the object 2 evaporates without trace, since itis an azeotropic cleansing composition which is non loaded withresidues.

The electronic control device 17 can incorporate a timer and/or athermoregulator for operating the heater 33.

EXAMPLE

A machine according to the invention has been realized in accordancewith the embodiment represented in the Figures with a width of 60 mmbetween the vertical longitudinal walls 3, 5 of the treating vessel 1, aheight and a length of the order of 85 cm. This treating vessel 1 allowsto receive a screen printing stencil having the form of a square platewith a side of 29 inches (73.66 cm). The machine has been used withVIGON® SC 200. The operating temperature was of 25° C. With such amachine, it is possible to treat successively three screen printingstencils for self-tensioning frames in one hour. The so-cleaned stencilsare perfectly clean and in perfect condition, and dry. Stencils soiledwith solder paste and/or stencils soiled with glue are successively oralternatively treated with a waiting time inferior to 1 minute betweentwo pieces.

What is claimed is:
 1. A method of cleaning objects having a generalform of plates, susceptible of being soiled with residues of averagedensity, and/or with solid residues of high density, and/or withresidues of low density, in which at least one object (2) to be cleanedis immersed in a vessel, so-called treating vessel (1), filled with aliquid cleansing composition, at least one (5) of vertical walls of thetreating vessel (1), so-called overflow wall (5), being constructed soas to form an overflow container into a second adjacent vessel,so-called overflow vessel (8), the overflow wall (5) being common to thetreating vessel (1) and the overflow vessel (8), at least a first flow(Q1) of cleansing composition is continuously extracted from thetreating vessel (1) and continuously reintroduced into the treatingvessel (1) after a passage through filtering means (31) for filteringresidues, and a second flow (Q2) of cleansing composition iscontinuously extracted from the overflow vessel (8) and continuouslyreintroduced into the treating vessel (1) after a passage throughfiltering means (38) for filtering residues, the method comprising thesteps of: providing a cleansing composition formed of a liquidazeotropic solution of a density at least equal to the density ofresidues of average density, so as to loosen residues from the object(2) without solubilizing them, placing at least one object (2)vertically in the treating vessel (1) having at least substantiallyvertical longitudinal walls (3, 5), spaced by a distance of less than 10cm, from at least substantially vertical main faces of the object (2) tobe cleaned, continuously extracting the cleansing composition both froma bottom part of the treating vessel (1) and from the overflow vessel(8), the whole cleansing composition extracted from the treating andoverflow vessels (1, 8) being continuously reintroduced in a top part ofthe treating vessel (1), after passing through said filtering means (31,38), the object being immersed into the cleansing composition whichcontinuously flows in the treating vessel (1) along the object (2)downwards with the first flow (Q1) so as to: allow the cleansingcomposition to loosen the residues from the object (2), allow thecleansing composition to carry along residues of average density andresidues of high density, allow flotation of the residues of low densityand overflow separation of the low density residues into the overflowvessel (8), so that in one continuous step residues are loosened fromthe object (2), and at least residues of low density being separated. 2.A method according to claim 1, wherein the cleansing compositioncomprises an aqueous solution for loosening the residues from the object(2) without solubilizing the residue.
 3. A method according to claim 1,wherein the cleaning composition has a density of the order of
 1. 4. Amethod according to claim 1, wherein the cleansing composition comprisesan aqueous solution of at least one constituent forming a microphase, ata temperature inferior to 50° C., and wherein the cleansing compositionis maintained at a treatment temperature that allows the formation ofthe microphase.
 5. A method according to claim 1, wherein the cleansingcomposition is reintroduced by spraying onto a free surface (41) of thecleansing composition contained in the treating vessel (1) from at leastone spraying ramp (34, 40), disposed at a height superior to that of theoverflow wall (5).
 6. A method according to claim 5, wherein thecleansing composition is diffused across the entire free surface (41).7. A method according to claim 5, wherein two spraying ramps (34, 40)parallel one to another are used, jets formed by one of the ramps (34)intersecting jets formed by another of the ramps (40) immediately aboveor at the level of said free surface (41) so as to form a cleansingcomposition screen having the effect of rinsing the object (2) beingextracted from the treating vessel (1).
 8. A method according to claim1, wherein the first flow (Q1) of cleansing composition extracted fromthe treating vessel (1) is adapted so that the retention time in thetreating vessel (1) is comprised between 30 seconds and 5 minutes.
 9. Amethod according to claim 1, wherein the treating vessel (1) comprisesvertical longitudinal walls (3, 5) spaced from the substantiallyvertical main faces (18, 19) of the object (2) by a distance comprisedbetween 1 to 5 cm.
 10. A method according to claim 1, wherein ultrasonicwaves are emitted in the treating vessel (1) in a direction at leastsubstantially perpendicular to a main plane of the object (2) placed inthe treating vessel (1).
 11. A machine for cleaning objects having ageneral form of plates, susceptible of being soiled with residues ofaverage density, and/or with solid residues of high density, and/or withresidues of low density, comprising a treating vessel (1), containing aliquid cleansing composition, and at least an object (2) to be cleanedimmersed into the cleansing composition, at least one (5) of verticalwalls of the treating vessel (1) being an overflow wall (5) constructedso as to form an overflow container in a second adjacent overflow vessel(8), an overflow wall (5) being common to the treating vessel (1) andthe overflow vessel (8), a first circulation means (28, 29, 30, 31, 32,33, 34) for extracting continuously at least a first flow (Q1) of thecleansing composition from the treating vessel (1) and for reintroducingthe cleansing composition continuously into the treating vessel (1)after a passage through a filtering means (31) for filtering residues,and a second circulation means (35, 36, 37, 38, 39, 49) for extractingcontinuously a second flow (Q2) of the cleansing composition from theoverflow vessel (8), and for reintroducing the cleansing compositioninto the treating vessel (1) after a passage through a filtering means(38) for filtering residues, wherein: the treating vessel (1) is shapedto receive at least one said object (2) to be cleaned in verticalposition, and to have at least substantially vertical longitudinal walls(3, 5), spaced by a distance inferior to 10 cm from vertical main facesof the object (2) to be cleaned, the first circulation means (28, 29,30, 31, 32, 33, 34) continuously extracting the cleansing compositionfrom a bottom part of the treating vessel (1) and continuouslyreintroducing the cleansing composition in a top part of the treatingvessel (1), the second circulation means (35, 36, 37, 38, 39, 33, 40)reintroducing in the top part of the treating vessel (1) the cleansingcomposition extracted from the overflow vessel (8), the firstcirculation means (28, 29, 30, 31, 32, 33, 34) maintaining in thetreating vessel (1) and along the object (2), the first flow (Q1) of thecleansing composition flowing downwards so as to: allow the cleaningcomposition to loosen the residues from the object (2), allow thecleansing composition to carry along the residues of average density andresidues of high density, allow flotation of the residues of low densityand overflow separation of the low density residues into the overflowvessel (8), so that as the cleansing composition is formed of a liquidazeotropic solution of a density at least substantially equal to thedensity of residues of average density, and loosens the residues fromthe object (2) without solubilizing the residues, in one continuousstep, the residues are loosened from the object (2), and at least theresidues of low density are separated.
 12. A machine according to claim11, wherein it comprises at least one spraying ramp (34, 40) forspraying the cleansing composition onto a free surface (41) of thecleansing composition contained in the treating vessel (1), thisspraying ramp (34, 40) being disposed at a level superior to that of theoverflow wall (5).
 13. A machine according to claim 12, wherein itcomprises two said spraying ramps (34, 40) parallel one to another, jetsformed by one ramp (34) intersecting jets formed by another of the ramps(40) immediately above or at level of said free surface (41) so as toform a cleansing composition screen structured to allow rinsing theobject (2) being extracted from the treating vessel.
 14. A machineaccording to claim 13, wherein the spraying ramps (34, 40) are disposedat least substantially above and perpendicularly to extreme upper edges(6, 7) of two vertical longitudinal walls (3, 5) of the treating vessel(1), at least one of which forms the overflow wall (5).
 15. A machineaccording to claim 13, wherein the first spraying ramp (34) belongs tothe first circulation means (28, 29, 30, 31, 32, 33, 34) and the secondspraying ramp (40) belongs to the second circulation means (35, 36, 37,38, 39, 33, 40).
 16. A machine according to claim 11, wherein theoverflowing wall (5) is formed of one of the vertical longitudinal walls(3, 5) of the treating vessel (1) an extreme upper edge (6) of which isat a height inferior to that of the extreme upper edges (7, 20, 21) ofthe other vertical walls (3, 11, 12) of the treating vessel (1).
 17. Amachine according to claim 11, wherein the treating vessel (1) hasvertical longitudinal walls (3, 5) spaced from vertical main faces (18,19) of the object (2) by a distance comprised between 1 and 5 cm.
 18. Amachine according to claim 11, wherein it comprises emission means (15,16) for emitting ultrasonic waves associated to at least one (3) of thevertical longitudinal walls (3, 5) of the treating vessel (1) so as toemit ultrasonic waves in the treating vessel (1) in a direction at leastsubstantially perpendicular to a main plane of the object (2) placed inthe treating vessel (1).
 19. A machine according to claim 11, wherein atleast one of the first (28, 29, 30, 31, 32, 33, 34) and second (35, 36,37, 38, 39, 33, 40) circulation means comprise thermoregulated heatingmeans (33) for heating the cleansing composition, disposed below thefiltering means (31, 38) for filtering residues, and abovereintroduction means (34, 40) for reintroducing the cleansingcomposition in a top part of the treating vessel (1).
 20. A machineaccording to claim 11, wherein the first circulation means (28, 29, 30,31, 32, 33, 34) comprise a first filter (21) and a first pump (32),wherein the second circulation means (35, 36, 37, 38, 39, 33, 40)comprise a second filter (38) and a second pump (39), wherein the firstfilter and the second filter are similar, and wherein the first andsecond pumps (32, 39) are similar.
 21. A machine according to claim 11,wherein the treating vessel (1) has the form of a parallelepiped, awidth comprised between 3 cm and 10 cm, and a volume comprised between10 l and 100 l.
 22. A machine according to claim 11, wherein itcomprises a suspension frame (22) for suspending the object (2) having aform of a flexible plate in the treating vessel, this suspension frame(22) being adapted to receive and maintain peripheral edges (24) of theobject (2).